Method of forming metallic film

ABSTRACT

A method of forming a metallic film is provided. The method includes: controlling gas conditions in a processing vessel in which a substrate is disposed on a stage; performing a pretreatment by spraying a plasma jet on the substrate in the processing vessel, the plasma jet being generated from gas containing an inert gas and hydrogen; and thermal spraying metallic material on the substrate while heating the stage at 100° C. or higher, the thermal spraying being performed after the pretreatment.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is based upon and claims priority to Japanese Patent Application No. 2018-070777 filed on Apr. 2, 2018, and Japanese Patent Application No. 2019-061645 filed on Mar. 27, 2019, the entire contents of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION 1. Field of the Invention

The present invention generally relates to a method of forming a metallic film.

2. Description of the Related Art

In order to improve adherence of a thermal sprayed film on a surface of a substrate, a method of pretreating a surface of a substrate before coating the surface with thermal sprayed film has been known (see Patent Document 1 and Patent Document 2, for example).

However, in the above mentioned conventional method, a surface of a substrate may be damaged by the pretreatment, and as a result, adherence of a thermal sprayed film on a surface of a substrate may degrade, and quality of the thermal sprayed film may degrade.

CITATION LIST Patent Document

-   [Patent Document 1] Japanese National Publication of International     Patent Application No. 2015-503031 -   [Patent Document 2] Japanese Laid-open Patent Application     Publication No. 05-086451

SUMMARY OF THE INVENTION

In one aspect, the present invention aims at providing a metallic film forming method capable of forming a metallic film having good adherence and low resistance, while suppressing damage to a surface of a substrate.

To solve the above problem, a method of forming a metallic film according to the present disclosure includes: controlling gas conditions in a processing vessel in which a substrate is disposed on a stage; performing a pretreatment by spraying, on the substrate in the processing vessel, a plasma jet generated from gas containing an inert gas and hydrogen; and thermal spraying metallic material on the substrate while heating the stage at 100° C. or higher. The thermal spraying is performed after the pretreatment.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional view of a plasma spraying apparatus according to an embodiment of the present disclosure, which illustrates an example of an overall structure of the plasma spraying apparatus;

FIG. 2 is a flowchart illustrating an example of a method of forming a metallic film according to the embodiment;

FIG. 3 illustrates measurement results of tensile strength of Cu films;

FIG. 4 illustrates measurement results of specific resistance of Cu films;

FIG. 5 illustrates cross sections of Cu films each formed at a different stage temperature; and

FIG. 6 is a diagram illustrating an application example of the method of forming a metallic film according to the present embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

In the following, embodiments of the present invention will be described with reference to the drawings. Note that in the following descriptions and the drawings, elements having substantially identical features are given the same reference symbols and overlapping descriptions may be omitted.

[Plasma Spraying Apparatus]

An example of a plasma spraying apparatus in which a method of forming a metallic film according to the present invention can be practiced will be described. FIG. 1 is a cross sectional view of a plasma spraying apparatus 1 according to an embodiment of the present disclosure, which illustrates an example of an overall structure of the plasma spraying apparatus.

The plasma spraying apparatus 1 injects feedstock powder of copper (Cu) (hereinafter referred to as “Cu powder R1”) from an opening lib of a tip of a nozzle 11. The Cu powder R1 is molten by heat of a plasma jet P formed from high-speed gas, and sprayed onto a surface of a substrate W. As a result, a Cu film F1 is formed on the surface of the substrate W. The substrate W is not limited to a specific type. The substrate W may be for example an insulating substrate on which a metallic film is formed, or a substrate for a power device. The Cu powder R1 is an example of feedstock powder. Feedstock powder according to the present embodiment is not limited to the Cu powder R1, and may be for example lithium (Li), aluminum (Al), copper (Cu), silver (Ag), gold (Au), and the like.

The plasma spraying apparatus 1 includes a supplying part 10, a gas supplying part 20, a plasma generating part 30, a processing vessel 40, a direct-current (DC) power source 50, a cooling device 60, a heating device 70 and a control unit 80.

The supplying part 10 includes the nozzle 11 and a feeder 12. The supplying part 10 conveys the Cu powder R1 via a plasma generating gas, and injects the Cu powder R1 from the opening of the tip of the supplying part 10. The feeder 12 supplies the Cu powder R1 to the nozzle 11. The Cu powder R1 is stored in a container 12 a in the feeder 12. The Cu powder R1 is fine powder having a particle diameter of 1 μm to 50 μm.

The feeder 12 includes an actuator 12 b. The nozzle 11 is a straight tubular member, and a passage 11 a for conveying the Cu powder R1 is formed inside the nozzle 11. The passage 11 a in the nozzle 11 is communicated with an inside of the container 12 a. As the container 12 a is vibrated by the actuator 12 b, the Cu powder R1 is entered from the container 12 a to the passage 11 a of the nozzle 11. In addition to the Cu powder R1, the plasma generating gas is supplied to the nozzle 11. The plasma generating gas is a gas for generating plasma. The plasma generating gas also acts as a carrier gas for conveying the Cu powder R1 through the passage 11 a.

The plasma generating gas is supplied from a gas supply source 21 in the gas supplying part 20. The plasma generating gas passes through a valve 22 controlled to be opened and/or closed, and a mass flow controller (MFC) for controlling a flow rate, and is conveyed to the passage 11 a of the nozzle 11 through a pipe 23. Argon (Ar) gas, helium (He) gas, nitrogen (N₂) gas, hydrogen (H₂) gas, or combinations of these gases may be used as the plasma generating gas. In the present embodiment, a case in which Ar gas is supplied as the plasma generating gas will be described.

The nozzle 11 runs through a main unit 13, and the tip of the nozzle 11 protrudes inside a plasma generating space U. The Cu powder R1 is conveyed to the tip of the nozzle 11 by plasma generating gas, and is injected, with the plasma generating gas, into the plasma generating space U from the opening 11 b of the tip.

The main unit 13 is formed of an insulating member. A through hole 13 a is provided at a central axis of the main unit 13, and a first half 11 c of the nozzle 11 is inserted into the main unit 13 through the through hole 13 a. As the DC power source 50 is connected to the first half 11 c of the nozzle 11, the first half 11 c of the nozzle 11 also acts as an electrode (cathode) for supplying current from the DC power source 50. The nozzle 11 is formed of metal, but the first half 11 c is insulated from other parts.

The plasma generating space U is a space mainly formed of a recess 13 b and a projection 13 d of the main unit 13. The tip of the first half 11 c of the nozzle 11 protrudes inside the plasma generating space U. The projection 13 d is connected at one end to a metal plate 13 c provided on an outer side surface of the main unit 13. As the DC power source 50 is connected to the metal plate 13 c, the metal plate 13 c and the projection 13 d act as an electrode (anode). Normally, the main unit 13 is electrically grounded. In this case, voltage of the anode may be ground voltage.

As electrical power of 500 W to 10 kW is supplied between the anode and the cathode, and discharge occurs between the tip of the nozzle 11 and the other end of the projection 13 d.

Accordingly, the plasma generating part 30 generates argon plasma from Ar gas injected from the nozzle 11 in the plasma generating space U.

Also, gas in which H₂ is added to Ar gas is supplied in the plasma generating space U. When the gas is supplied in the plasma generating space U, the gas generates a rotational flow. The gas in which H₂ is added to Ar gas is supplied from a gas supply source 24 under control of a valve 25 and a mass flow controller (MFC), and is supplied to the plasma generating space U through a pipe 26 and through an inside of the main unit 13. The gas enters the plasma generating space U in a lateral direction.

In FIG. 1, only a single gas supplying path for the gas in which H₂ is added to Ar gas is illustrated. However, in reality, multiple gas supply paths for introducing the gas are provided in the main unit 13. Accordingly, the gas in which H₂ is added to Ar gas is supplied into the plasma generating space U from the multiple gas supply paths, and the gas supplied from the multiple gas supply paths generates a rotational flow in the plasma generating space U. Because of the rotational flow, diffusion of generated plasma is prevented, and the plasma jet P is linearly emitted. In the plasma generating part 30, the plasma generating gas injected from the tip of the nozzle 11 is decomposed, and the plasma jet P is generated. The plasma jet P generated here has a common axis O with the nozzle 11. “Having a common axis” in the present embodiment means that a central axis of the supplying part 10 (nozzle 11) coincides (or substantially coincides) with a central axis of a spraying direction of the plasma jet P.

According to the configuration of the plasma spraying apparatus 1, the supplying part 10 causes the Cu powder R1 and Ar gas to pass straight in the passage 11 a formed inside the nozzle 11, and the Cu powder R1 and Ar gas are injected from the opening 11 b of the tip of the nozzle 11. The injected Cu powder R1 is molten by heat of the plasma jet P formed by high-speed Ar gas. Also, as the molten Cu is sprayed onto a surface of the substrate W, the Cu film F1 is formed on the substrate W by thermal spraying.

The processing vessel 40 is a cylindrical hollow container, and is formed of aluminum, stainless steel, or quartz, for example. The processing vessel 40 supports the main unit 13 at a ceiling of the processing vessel 40, and makes the supplying part 10 and the plasma generating part 30 enclosed regions. The substrate W is placed on a stage 41 provided at a bottom 40 a of the processing vessel 40. The stage 41 may be an XY stage, for example. When the stage 41 is an XY stage, thermal spray can be applied to the substrate W while moving the substrate W. Thus, as thermal sprayed film can be formed in a wide area, productivity increases.

A window 42, a gate valve 43, an evacuating line 47, and a port 48 are provided at a side wall of the processing vessel 40. The window 42 is used for looking inside of the processing vessel 40. The gate valve 43 is used for loading the substrate W into the processing vessel 40 and/or unloading the substrate W from the processing vessel 40 to outside. An exhaust device 44 and a collection/disposal device 45 are provided at the evacuating line 47. An inside of the processing vessel 40 is decompressed to a predetermined pressure by the exhaust device 44. It is preferable that the collection/disposal device 45 is disposed between the processing vessel 40 and the exhaust device 44. The collection/disposal device 45 draws gas and the Cu powder R1 in the processing vessel 40, and discards the Cu powder R1. The collection/disposal device 45 may be included in the exhaust device 44. In a case in which the exhaust device 44 is a water-sealed vacuum pump, the exhaust device 44 can absorb the Cu powder R1 into oil of the pump. Further, between the processing vessel 40 and the collection/disposal device 45, a valve 46 for controlling a communication state of the evacuating line 47 is provided. An oxygen densitometer 49 is connected to the port 48. The oxygen densitometer 49 measures oxygen concentration of gas inside the processing vessel 40. The oxygen densitometer 49 takes in gas inside the processing vessel 40 by a pump in the oxygen densitometer 49, for example. A location where oxygen concentration is measured may be near the port 48, but it is more preferable that oxygen concentration near the substrate W can be measured by attaching an induction tube 49 a to the oxygen densitometer 49. An example of the oxygen densitometer 49 is a zirconia type oxygen densitometer.

The cooling device 60 includes a chiller unit 61, a coolant pipe 62, a coolant passage 63, a coolant pipe 64, and valves 65 and 66. The coolant passage 63 is formed inside the main unit 13. Coolant (such as cooling water) that is supplied from the chiller unit 61 circulates in the coolant pipe 62, the coolant passage 63, and the coolant pipe 64 in accordance with a control of the valves 65 and 66, and returns to the chiller unit 61. The coolant cools the main unit 13 and prevents the main unit 13 from being overheated by heat of plasma.

The heating device 70 includes a heater 71 embedded in the stage 41 provided in the processing vessel 40, and a power source 72 for supplying electric power to the heater 71. Note that the heating device 70 may only be a means that is capable of adjusting temperature of the stage 41. For example, in another embodiment, the heating device 70 may be configured to cause a heating medium controlled to be at a given temperature to circulate in the stage 41.

The control unit 80 controls each element in the plasma spraying apparatus 1. Specifically, the control unit 80 controls the gas supplying part 20 (gas supply sources 21 and 24, and valves 22 and 25), the feeder 12 (actuator 12 b), the processing vessel 40 (stage 41, gate valve 43, exhaust device 44, collection/disposal device 45, and valve 46), the DC power source 50, the cooling device 60 (chiller unit 61), the heating device 70 (power source 72), and the like.

The control unit 80 includes a CPU, a ROM (Read Only Memory), a RAM (Random Access Memory), and an HDD (Hard Disk Drive). The CPU selects a recipe or a program for plasma spraying of specific metal feedstock, and loads it onto the RAM. The CPU sends control signals to each element based on the program loaded on the RAM. By an operation of the control unit 80, a Cu film having desired characteristics can be formed on the substrate W by thermal spraying. The control unit 80 may be implemented by software or hardware.

[Method of Forming Metallic Film]

An example of a method of forming a metallic film according to the present embodiment will be described. The method to be described below is embodied by the control unit 80 controlling each element in the plasma spraying apparatus 1. FIG. 2 is a flowchart illustrating the example of the method of forming a metallic film according to the present embodiment.

First, a loading step S101 of placing the substrate W on the stage 41 in the processing vessel 40 is performed. In the present embodiment, after the gate valve 43 is opened, the substrate W is placed on the stage 41 in the processing vessel 40 by using a loading mechanism (not illustrated).

After the loading step S101, a gas composition controlling step S102 of controlling gas composition in the processing vessel 40 is performed. In the present embodiment, after the gate valve 43 is closed, the inside of the processing vessel 40 is decompressed to a predetermined pressure by the exhaust device 44, and purging is performed by using an inert gas. By performing the gas composition controlling step S102, the inside of the processing vessel 40 may preferably be set to a gas composition in which oxygen concentration is 100 ppm or less, in order to prevent metallic material for thermal spraying from being oxidized by oxygen or moisture. More preferably, the oxygen concentration may be set to 30 ppm or less. As a method of reducing oxygen concentration in the processing vessel 40 to 100 ppm or less, cycle purging can be employed. Cycle purging is a method of repeating a cycle of a step of evacuating the processing vessel 40, a step of pressurizing the processing vessel 40 by introducing an inert gas, and a step of evacuating the processing vessel 40. In the present embodiment, cycle purging is performed in a manner to be described below. First, the inside of the processing vessel 40 is evacuated at approximately 90 Torr (approximately 12 kPa). Second, the processing vessel 40 is pressurized by introducing Ar gas from a gas supplying unit (not illustrated) to atmospheric pressure. Third, the inside of the processing vessel 40 is evacuated again. The above second and third steps are executed repeatedly. Also, in parallel with the repeated execution of the second and third steps, oxygen concentration in the processing vessel 40 is measured by the oxygen densitometer 49, which is connected to the port 48 positioned at a different location of the evacuating line 47. The oxygen densitometer 49 takes in gas from inside of the processing vessel 40 by a pump in the oxygen densitometer 49. A location where the oxygen concentration is measured may be near the port 48, but it is more preferable that oxygen concentration near the substrate W can be measured by attaching an induction tube 49 a to the oxygen densitometer 49. An example of the oxygen densitometer 49 is a zirconia type oxygen densitometer. When the measured oxygen concentration reaches a value sufficiently lower than 100 ppm, the cycle purging is finished. After the cycle purging, the inside of the processing vessel 40 may be maintained at an evacuated state, or the pressure in the processing vessel 40 may be changed and maintained to a predetermined pressure by introducing Ar gas into the processing vessel 40 by the gas supplying unit (not illustrated). When the above described process has been performed, the gas composition controlling step S102 is finished.

After the gas composition controlling step S102, a temperature elevation step S103 of raising a temperature of the stage 41 is performed. In the present embodiment, a temperature of the stage 41 is raised by the heating device 70. By performing the temperature elevation step S103, a temperature of the stage 41 may preferably be raised to 100° C. or higher. More preferably, the temperature may be raised to 150° C. or higher. Note that the temperature elevation step S103 may be performed before (or in parallel with) the gas composition controlling step S102. By performing the gas composition controlling step S102 and the temperature elevation step S103 at the same time, a time required for performing the gas composition controlling step S102 and the temperature elevation step S103 can be shortened, and productivity increases. Further, if a temperature of the stage 41 can be raised to 100° C. or higher at a pretreatment step S105 (to be described below), execution of the temperature elevation step S103 may be omitted. By omitting execution of the temperature elevation step S103, a time for performing the temperature elevation step S103 becomes unnecessary, and productivity increases.

After the temperature elevation step S103, a pressure controlling step S104 of adjusting pressure in the processing vessel 40 is performed. In the present embodiment, pressure in the processing vessel 40 is adjusted to a predetermined pressure (such as several tens of kPa) by introducing an inert gas from the gas supplying unit (not illustrated).

After the pressure controlling step S104, a pretreatment step S105 of spraying, on the substrate W, a plasma jet generated from gas in which H₂ is added to an inert gas is performed. In the present embodiment, an inert gas (Ar gas) is supplied to the processing vessel 40 from the gas supply source 21 through the pipe 23 and the nozzle 11, another gas (gas in which H₂ is added to Ar gas) is supplied to the processing vessel 40 from the gas supply source 24 through the pipe 26, and voltage is applied between the anode and the cathode from the DC power source 50. By performing the pretreatment step S105, an oxide film formed on a surface of the substrate W can be removed. Further, in the pretreatment step S105, it is preferable to spray a plasma jet P on the substrate W while moving the stage 41. If the plasma jet is sprayed on the substrate W while moving the stage 41, a pretreatment can be applied to a wide area all at once, and productivity increases. Note that, in the pretreatment step S105, the Cu powder R1 from the feeder 12 is not supplied to the nozzle 11.

By the pressure controlling step S104, a pressure in the processing vessel 40 may preferably be set at 150 to 500 Torr (20 to 67 kPa). More preferably, the pressure may be set at 200 to 400 Torr (27 to 53 kPa).

A flow rate of Ar gas from the gas supply source 21 is between 10 and 40 L/min. An appropriate flow rate of Ar gas varies depending on material of powder or an average particle diameter of powder. In a case in which the Cu powder R1 according to the present embodiment is used, it is preferable that the flow rate is between 10 and 15 L/min.

A flow rate of gas supplied from the gas supply source 24 in which H₂ is added to Ar gas may preferably be between 10 and 20 L/min. A preferable H₂ concentration of the gas is 5% or less. However, from the gas supply source 24, Ar gas (gas which does not contain H₂) may be supplied.

After the pretreatment step S105, a thermal spraying step S106 of thermal spraying metallic material on the substrate W, while heating the stage 41 at 100° C. or higher, is performed. In the present embodiment, while heating the stage 41 at 100° C. or higher, Ar gas is supplied to the processing vessel 40 from the gas supply source 21 through the pipe 23 and the nozzle 11, Ar gas or another gas (gas in which H₂ is added to Ar gas) is supplied to the processing vessel 40 from the gas supply source 24 through the pipe 26, voltage is applied between the anode and the cathode from the DC power source 50 to cause discharge, and the Cu powder R1 is supplied from the feeder 12 to the nozzle 11. By performing the above operations, Cu thermal sprayed film is formed on the substrate W. Further, in the thermal spraying step S106, it is preferable to spray a plasma jet P on the substrate W while moving the stage 41. If the plasma jet is sprayed on the substrate W while moving the stage 41, the Cu thermal sprayed film can be formed on a wide area all at once.

Further, in the thermal spraying step S106, in order to improve adherence of the substrate W and Cu thermal sprayed film on a surface of a substrate, a temperature of the stage 41 may preferably be set to 150° C. or higher. Also, considering a heatproof temperature of a device, a temperature of the stage 41 may preferably be set to 400° C. or less. More preferably, the temperature may be set to 280° C. or less.

A pressure in the processing vessel 40 may preferably be set at 150 to 500 Torr (20 to 67 kPa). More preferably, the pressure may be set at 200 to 400 Torr (27 to 53 kPa).

A flow rate of Ar gas from the gas supply source 21 is between 10 and 40 L/min. An appropriate flow rate of Ar gas varies depending on material of powder or an average particle diameter of powder. In a case in which the Cu powder R1 according to the present embodiment is used, it is preferable that the flow rate is between 10 and 15 L/min.

A flow rate of Ar gas (or another gas in which H₂ is added to Ar gas) supplied from the gas supply source 24 may preferably be between 10 and 20 L/min. In a case in which gas in which H₂ is added to Ar gas is used, a preferable H₂ concentration of the gas is 5% or less.

After the thermal spraying step S106, a temperature lowering step S107 of lowering a temperature of the stage 41 is performed. In the present embodiment, a temperature of the stage 41 is lowered by the cooling device 60 to a predetermined temperature (such as room temperature).

After the temperature lowering step S107, an unloading step S108 of unloading the substrate W placed on the stage 41 from the processing vessel 40 is performed. In the present embodiment, after the gate valve 43 is opened, the substrate W placed on the stage 41 is unloaded out of the processing vessel 40 by using a loading mechanism (not illustrated). By performing the above mentioned steps (S101 to S108), Cu thermal sprayed film is formed on the substrate W.

In the above described method of forming a metallic film according to the present embodiment, the pretreatment step S105, in which a plasma jet generated from Ar gas or gas in which H₂ is added to Ar gas is sprayed on the substrate W placed on the stage 41 in the processing vessel 40 that is in a low oxygen concentration atmosphere, is performed. After the pretreatment step S105, the thermal spraying step S106, in which Cu powder is thermal sprayed on the substrate W placed on the stage 41 in the processing vessel 40 that is in a low oxygen concentration atmosphere, is performed while heating the stage 41 at 100° C. or higher. As the pretreatment step S105 and the thermal spraying step S106 are performed successively under a low oxygen concentration atmosphere, an oxide film formed on a surface of the substrate W can be removed by the pretreatment step S105, and a Cu thermal sprayed film can be formed on the surface of the substrate W in a state in which an oxide film is removed from the surface. Thus, a Cu thermal sprayed film of good adherence can be formed. In addition, as a Cu thermal sprayed film can be formed on a clean surface of the substrate W in which an oxide film is removed, a Cu thermal sprayed film including few voids (small gaps) and having low resistance can be formed.

EXAMPLES

In the following, results of evaluations of film characteristics of a Cu thermal sprayed film formed by the method of forming a metallic film according to the present embodiment will be described.

Example 1

In Example 1, experiments for forming a Cu film (which is an example of a metallic film) on a chip having an Al film (which is an example of a substrate W) were performed. The experiments were performed while changing conditions of oxygen concentration, a process gas, magnitude of electric current, and a temperature of the stage 41 when performing the thermal spraying step S106.

With respect to oxygen concentration, a case in which oxygen concentration in the processing vessel 40 is the same as air (approximately 21%) without performing cycle purging, a case in which oxygen concentration in the processing vessel 40 is approximately 1% (this environment is made by replacing air in the processing vessel 40 with Ar gas and by setting a pressure in the processing vessel to the same as atmospheric pressure, although cycle purging is not performed), and a case in which oxygen concentration in the processing vessel 40 is lowered to approximately 10 ppm by performing cycle purging, were evaluated. Note that the oxygen concentration was measured by the oxygen densitometer as described above. Also, the above mentioned process gas includes gas supplied from the gas supply source 21 and the gas supply source 24, as used in the pretreatment step S105 and the thermal spraying step S106. The process gas is Ar gas or process gases that are Ar gas and gas in which H₂ is added to Ar gas. In cases in which H₂ is added, H₂ is added to Ar gas supplied from the gas supply source 24. The above mentioned magnitude of electric current is electric current supplied from the DC power source 50. The above mentioned temperature of the stage 41 represents a temperature of the stage 41 when thermal spraying is started at the thermal spraying step S106 (in the following description, the temperature of the stage 41 at the thermal spraying step S106 may be referred to as a “stage temperature”).

Also, in each of the experiments of Example 1, a test sample (may also be referred to as a sample) in which a pin (a diameter of which is 2 mm) was joined on the Cu film of the chip via solder was made, and tensile strength was measured to evaluate adherence between the Cu film and a lower layer. The measurement of tensile strength was performed in the following manner. First, the test sample was fixed (via solder) on a plate for placing the test sample. Next, by pulling the pin, having a diameter of 2 mm, upward, a tensile load was applied. By increasing the tensile load gradually, a tensile load when the test sample was broken was measured. The tensile strength in Example 1 is the tensile load when the test sample was broken (unit of the tensile strength is N). After the tensile strength has been measured, a location of the test sample having been broken was identified.

Results of measuring the tensile strength of a Cu film are illustrated in FIG. 3. As described above, in Example 1, multiple test samples (samples A to G) were made by changing conditions (oxygen concentration, a process gas, magnitude of electric current, and a stage temperature) in the thermal spraying step S106. Note that the sample H in FIG. 3 is a test sample in which a Cu film is formed by sputtering, which is made as a comparative example.

A row of “OXYGEN CONCENTRATION” in FIG. 3 represents oxygen concentration in the processing vessel 40 at the thermal spraying step S106 when the test samples were made.

A row of “PROCESS GAS” in FIG. 3 represents the process gas used in the thermal spraying step S106 when the test samples were made. Note that both gas supplied from the gas supply source 21 and gas supplied from the gas supply source 24 are illustrated in the row of “PROCESS GAS” (this is the same as in FIG. 4).

A row of “ELECTRIC CURRENT” in FIG. 3 represents the magnitude of electric current supplied in the thermal spraying step S106 when the test samples were made.

A row of “TEMPERATURE” in FIG. 3 represents a stage temperature (temperature of the stage 41 at the thermal spraying step S106) when the test samples were made.

As the results of the experiments, tensile strength of each of the samples is illustrated in a graph of FIG. 3. Each bar in the graph represents an average tensile strength, and a range of a maximum and minimum of the tensile strength is illustrated as an error bar.

A Cu thermal sprayed film of the sample A was formed at thermal spraying step S106 under conditions that oxygen concentration was approximately 21%, that a process gas was Ar gas only, that magnitude of electric current was 200 A, and that a stage temperature was approximately 80° C.

A Cu thermal sprayed film of the sample B was formed at thermal spraying step S106 under conditions that oxygen concentration was approximately 1%, that a process gas was Ar gas only, that magnitude of electric current was 200 A, and that a stage temperature was approximately 80° C.

A Cu thermal sprayed film of the sample C was formed at thermal spraying step S106 under conditions that oxygen concentration was approximately 10 ppm, that a process gas was Ar gas only, that magnitude of electric current was 250 A, and that a stage temperature was 200° C. or less.

A Cu thermal sprayed film of the sample D was formed at thermal spraying step S106 under conditions that oxygen concentration was approximately 10 ppm, that process gases were Ar gas and gas in which H₂ of 5% concentration is added to Ar gas, that magnitude of electric current was 200 A, and that a stage temperature was 20° C.

A Cu thermal sprayed film of the sample E was formed at thermal spraying step S106 under conditions that oxygen concentration was approximately 10 ppm, that process gases were Ar gas and gas in which H₂ of 5% concentration is added to Ar gas, that magnitude of electric current was 200 A, and that a stage temperature was 100° C.

A Cu thermal sprayed film of the sample F was formed at thermal spraying step S106 under conditions that oxygen concentration was approximately 10 ppm, that process gases were Ar gas and gas in which H₂ of 5% concentration is added to Ar gas, that magnitude of electric current was 200 A, and that a stage temperature was 150° C. or higher.

A Cu thermal sprayed film of the sample G was formed at thermal spraying step S106 under conditions that oxygen concentration was approximately 10 ppm, that process gases were Ar gas and gas in which H₂ of 5% concentration is added to Ar gas, that magnitude of electric current was 250 A, and that a stage temperature was 150° C. or higher.

Also, as described above, the sample H is a test sample in which a Cu film is formed by sputtering, which is made as a comparative example.

As can be seen from the results of the sample A and the sample B, by reducing oxygen concentration from approximately 21% to approximately 1%, the tensile strength improves. That is, it is considered that adherence between the Cu thermal sprayed film and the Al film improves, by reducing oxygen concentration from approximately 21% to approximately 1%.

As can be seen from the results of the sample B and the sample C, by reducing oxygen concentration from approximately 1% to approximately 10 ppm, by changing magnitude of electric current from 200 A to 250 A, and by changing a stage temperature from approximately 80° C. to 200° C., the tensile strength improves. That is, it is considered that adherence between the Cu thermal sprayed film and the Al film improves, by reducing oxygen concentration from approximately 1% to approximately 10 ppm, by changing magnitude of electric current from 200 A to 250 A, and by changing a stage temperature from approximately 80° C. to 200° C.

As can be seen from the results of the sample D, the sample E and the sample F, by raising a stage temperature, the tensile strength improves. That is, it is considered that adherence between the Cu thermal sprayed film and the Al film improves, by raising a stage temperature.

As can be seen from the results of the sample F and the sample G, by increasing electric current, the tensile strength improves. That is, it is considered that adherence between the Cu thermal sprayed film and the Al film improves, by increasing electric current.

As can be seen from the results of the sample C and the sample G, by changing a process gas from Ar gas to gas in which H₂ of 5% concentration is added to Ar gas, the tensile strength improves. That is, it is considered that adherence between the Cu thermal sprayed film and the Al film improves, by using a gas containing Ar gas and H₂ as a process gas.

As can be seen from the results of the sample G and the sample H, by performing thermal spraying of Cu under conditions that oxygen concentration is approximately 10 ppm, that process gases are Ar gas and gas in which H₂ of 5% concentration is added to Ar gas, that magnitude of electric current is 250 A, and that a stage temperature is 150° C. or higher, a Cu thermal sprayed film having higher tensile strength than a Cu sputtered film can be formed. That is, it is considered that adherence of the Cu thermal sprayed film formed under the above described condition becomes stronger than a Cu sputtered film with respect to adherence between a Cu film and an Al film.

Example 2

In Example 2, experiments for forming a Cu thermal sprayed film (which is an example of a metallic film) on an A1 ₂O₃ plate (which is an example of a substrate W) were performed. The experiments were also performed while changing conditions of oxygen concentration, a process gas, and presence or absence of a surface smoothing treatment when performing the thermal spraying step S106. Further, in the experiments, a thickness of a Cu thermal sprayed film was measured by a micrometer (a diameter of a surface to be measured was 6.3 mm), sheet resistance of the Cu thermal sprayed film was measured by using 4-point probes (a distance between adjacent probes was 2 mm), and specific resistance of the Cu thermal sprayed film was calculated by multiplying the measured thickness of the Cu thermal sprayed film and the measured sheet resistance. Note that the above mentioned surface smoothing treatment means a polishing treatment to eliminate an adverse effect on sheet resistance that is caused by roughness of a surface of a Cu thermal sprayed film. By performing the surface smoothing treatment, a more accurate resistance (specific resistance) of a Cu thermal sprayed film can be measured.

Results of measuring the specific resistance of Cu films are illustrated in FIG. 4. In FIG. 4, specific resistance (μΩ·cm) of Cu thermal sprayed films of test samples I, J, K, and L are illustrated. As described above, the Cu thermal sprayed films of the respective test samples I, J, K, and L were formed under different conditions.

The Cu thermal sprayed film of the sample I was formed at thermal spraying step S106 under conditions that oxygen concentration was approximately 1% or 21%, and that a process gas was Ar gas only. Also, the surface smoothing treatment was not performed.

The Cu thermal sprayed film of the sample J was formed at thermal spraying step S106 under conditions that oxygen concentration was approximately 10 ppm, and that a process gas was Ar gas only. Also, the surface smoothing treatment was not performed.

The Cu thermal sprayed film of the sample K was formed at thermal spraying step S106 under conditions that oxygen concentration was approximately 10 ppm, and that process gases were Ar gas and gas in which H₂ of 5% concentration is added to Ar gas. Also, the surface smoothing treatment was not performed.

The Cu thermal sprayed film of the sample L was formed at thermal spraying step S106 under conditions that oxygen concentration was approximately 10 ppm, and that process gases were Ar gas and gas in which H₂ of 5% concentration is added to Ar gas. Also, the surface smoothing treatment was performed.

As can be seen from the results of the sample I and the sample J, by changing oxygen concentration from approximately 1% or higher to approximately 10 ppm, specific resistance decreases from a range between 13 and 20 μΩ·cm to a range between 5.2 and 6.4 μΩ·cm.

As can be seen from the results of the sample J and the sample K, by using Ar gas and another gas in which H₂ of 5% concentration is added to Ar gas, as process gases, specific resistance decreases from a range between 5.2 and 6.4 μΩ·cm to a range between 3.3 and 3.4 μΩ·cm.

As can be seen from the results of the sample K and the sample L, by performing the surface smoothing treatment, specific resistance decreases from a range between 3.3 and 3.4 μΩ·cm to 1.8 μΩ·cm. That is, it is considered that roughness of a surface of a Cu thermal sprayed film increases specific resistance by approximately 1.5 to 1.6 μΩ·cm.

Example 3

In Example 3, experiments for forming a

Cu thermal sprayed film (which is an example of a metallic film) on an Al—Si film (which is an example of a substrate W) were performed, while changing a stage temperature. Note that the experiments were performed under conditions that oxygen concentration was approximately 10 ppm, and that process gases were Ar gas and gas in which H₂ of 5% concentration is added to Ar gas. A stage temperature was controlled by the heating device 70 and by controlling supply of cooling water of 20° C. from the cooling device 60. Also, in the experiments, a cross surface of the Cu thermal sprayed film was observed by using a scanning electron microscope (SEM).

Cross sections of the Cu thermal sprayed films formed in the experiments of Example 3 are illustrated in FIG. 5. In FIG. 5, cross sections of Cu thermal sprayed films of test samples M, N, and O are illustrated. As described above, the Cu thermal sprayed films of the respective test samples M, N, and O were formed under different stage temperatures.

The Cu thermal sprayed film of the sample M was formed by controlling a stage temperature (temperature of the stage 41 when thermal spraying is started) at approximately 20° C.

The Cu thermal sprayed film of the sample N was formed by controlling a stage temperature at approximately 100° C.

The Cu thermal sprayed film of the sample O was formed by controlling a stage temperature at 150° C. or higher.

As can be seen from the results of the samples M, N, and O, if a stage temperature is high, a Cu thermal sprayed film having less voids can be formed.

[Application Example of Method of Forming Metallic Film]

An application example of the method of forming a metallic film according to the present embodiment will be described, by exemplifying a case in which a Cu thermal sprayed film (an example of a metallic film) is applied to an IGBT (Insulated Gate Bipolar Transistor) module. FIG. 6 is a diagram illustrating the application example of the method of forming a metallic film according to the present embodiment. Specifically, a cross section of an IGBT module 100 is illustrated in FIG. 6.

The IGBT module 100 is an example of a power module. An insulating substrate 102 on which a circuit pattern 103 is formed is soldered on a heat dissipation plate 101. On the circuit pattern 103, a silicon chip 104 is soldered. As the heat dissipation plate 101, a Cu thermal sprayed film that is formed by the aforementioned method of forming a metallic film is used, for example. As the insulating substrate 102, a ceramic plate such as alumina or aluminum nitride may be used.

On a bottom surface of the silicon chip 104, a collector electrode 104 c is formed. The collector electrode 104 c is electrically connected to the circuit pattern 103. As the circuit pattern 103, a Cu thermal sprayed film that is formed by the aforementioned method of forming a metallic film is used, for example. Accordingly, as a Cu thermal sprayed film can be formed by a dry process, the IGBT module 100 can be manufactured at a shorter time and at a lower cost, as compared to a heat dissipation substrate formed by bonding a copper circuit board on an insulating substrate by means of DCB (Direct Copper Bonding) method.

On an upper surface of the silicon chip 104, an emitter electrode 104 e is formed. The emitter electrode 104 e is electrically connected to a circuit board 108 via an electrode film 105 and wires 106. As the wires 106, a Cu thermal sprayed film that is formed by the aforementioned method of forming a metallic film is used, for example.

On an upper surface of the silicon chip 104, a gate electrode 104 g is also formed. The gate electrode 104 g is electrically connected to a circuit board 108 via a wire 107. As the wire 107, a Cu thermal sprayed film that is formed by the aforementioned method of forming a metallic film is used, for example.

In order to protect the silicon chip 104, the electrode film 105, the wire 106, and the wire 107, a region over the silicon chip 104 is sealed and protected with resin such as silicone or with a cover (not illustrated).

As described above, a Cu thermal sprayed film that is formed by the method of forming a metallic film according to the present embodiment is applicable to the heat dissipation plate 101, the circuit pattern 103, the wires 106 and 107, and the like. As a Cu thermal sprayed film has good adherence and low resistance, a highly reliable IGBT module 100 can be manufactured by employing the Cu thermal sprayed film.

Embodiments for practicing the present invention have been described in the above. However, the present invention is not limited to the above described embodiments. Various changes or enhancements can be made hereto within the scope of the present invention.

The above described embodiments have described a case in which plasma spraying is applied to a substrate W. However, plasma spraying according to the present embodiment is applicable to other materials, such as a rolled electrode sheet, or various types of substrates used in an LCD (Liquid Crystal Display), an FPD (Flat Panel Display), and the like. 

What is claimed is:
 1. A method of forming a metallic film, the method comprising: controlling gas conditions in a processing vessel in which a substrate is disposed on a stage; performing a pretreatment by spraying a plasma jet on the substrate in the processing vessel, the plasma jet being generated from gas containing an inert gas and hydrogen; and thermal spraying metallic material on the substrate while heating the stage at a temperature of 100° C. or higher, the thermal spraying being performed after the pretreatment.
 2. The method according to claim 1, further comprising raising a temperature of the stage to 100° C. or higher, before the thermal spraying.
 3. The method according to claim 1, wherein, in the controlling of the gas conditions in the processing vessel, oxygen concentration in the processing vessel is set to 100 ppm or less.
 4. The method according to claim 1, wherein the stage is an XY stage, and in the pretreatment, the plasma jet is sprayed on the substrate while moving the XY stage.
 5. The method according to claim 1, wherein the stage is an XY stage, and in the thermal spraying, the metallic material is sprayed on the substrate while moving the XY stage.
 6. The method according to claim 1, wherein the substrate is an insulating substrate having another metallic film on a surface of the insulating substrate, and in the thermal spraying, the metallic material is sprayed on a surface of said another metallic film.
 7. The method according to claim 1, wherein the substrate is an insulating substrate, and in the thermal spraying, the metallic material is sprayed on a surface of the insulating substrate. 